Retorting of oil shale

ABSTRACT

SHALE OIL OF IMPROVED QUALITY IS RECOVERED FROM OIL SHALE RETORTED IN A PLURAL STAGE RETORTING SYSTEM AT AN ELEVATED TEMPERATURE IN THE PRESENCE OF AN INERT GAS UNDER AN ELEVATED PRESSURE.

United States Patent O 3,573,194 RETORTING OF OIL SHALE Jack R. Hopper,East Baton Rouge Parish, La., and Edward L. Wilson, Jr., Baytown, andNick P. Peet, Houston, Tex.; said Peet assignor to Esso Research andEngineering Company Filed Mar. 26, 1969, Ser. No. 810,577 Int. Cl. `Cb53/06 U.S. Cl. 208--11 11 Claims ABSTRACT OF THE DISCLOSURE Shale oil ofimproved quality is recovered from oil shale retorted in a plural stageretorting system at an elevated temperature in the presence of an inertgas under an elevated pressure.

BACKGROUND OF THE INVENTION (1) Field ofthe invention The presentinvention is directed to retorting of oil shale. More particularly, theinvention is concerned with retorting of oil shale at elevated pressuresin the presence of an inert gas. In its more specific aspects, theinvention is concerned with inert gas pressure retorting of crushed oilshale at elevated temperature to obtain shale oil of improved productquality.

(2) Description of the prior art It is known to retort oil shale underpressure where the whole system is pressurized. It is also known toretort oil shale under pressure in the presence of hydrogen. Heretofore,noncondensable gas has been used in low presssure retorting of oilshale. Retorting of oil shale in the presence of hydrogen improves theproduct quality of shale oil. However, it has not been known heretoforethat retorting of oil shale under pressure with an inert gas would alsoimprove the product quality comparable to that obtained with hydrogenwhich at least partially hydrogenated the shale oil. The use of an inertgas at elevated temperature is unobvious and allows the obtaining ofmarked advantages. Also, the pressurization of the retort only in aplural stage system is advantageous in that the other stages may beoperated at low pressures and still obtain the benefit of high pressure.Prior art considered with respect to this invention include thefollowing listed U.S. patents: U.S. 1,734,970, U.S. 1,941,809, U.S.2,452,634, U.S. 2,601,257, U.S. 2,665,238, U.S. 2,812,288, U.S. 2,-911,349, U.S. 2,991,164, U.S. 3,117,072, U.S. 3,118,746, U.S. 3,361,644,U.S. 3,384,569.

SUMMARY OF THE INVENTION The present invention is directed to retortingof oil shale. More particularly, the invention is concerned withretorting of crushed oil shale at elevated temperatures and pressures.In its more specific aspects, the invention is concerned with retortingof crushed oil shale at an elevated pressure in the presence of an inertgas wherein the retorting zone of a plural stage retorting system ismaintained at an elevated pressure while the other zones are maintainedat substantially lower pressure to obtain improved quality of the oilshale.

VARIABLES OF THE INVENTION In the practice of the present invention,temperatures in the preheating zone may range from about 400 F. t0 about800 F. with a suitable temperature being about 600 F. A hot gas at about1000 F. may serve to preheat the fresh oil shale which may be introducedat a temperature of about 80 F.

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Temperatures in the retorting zone may range from about 600 F. to about1000 F. with a temperature suitably about 900 F. Inert gas may beintroduced into the retorting zone. The amount of the inert gasintroduced into the retorting zone may range from about 5,000 to about15,000 cu. ft. per ton of raw oil shale with about 10,000 cu, ft. ofinert content gas per ton of raw oil shale being satisfactory. The inertgas may be preheated to temperatures up to 1200 F.

In the burning zone, the temperature may range from about l000 F. toabout 1400" F. and suitably air at about F. in an amount of about 3,000to about 6,000 cu. ft. per ton of raw oil shale may be introduced. About4,000 cu. ft. of air per ton of raw oil shale may be used. The air maybe at about 80 F. Other free oxygen-containing gases having a greatercontent of free oxygen than air may be used.

Temperatures in the cooling zone may range from about 1400 F. to about200 F. with an inert gas being introduced thereinto for coolingpurposes. Thus, the spent shale may enter the cooling zone at 1400 F.and may leave the cooling zone at 400 F'. with about 12,000 to about20,000 cu. ft. of the gas per ton of raw oil shale being used. About18,000 cu. ft. of the inert gas per ton of raw oil shale may besatisfactory.

The pressure on the retorting zone is suitably maintained by injectionof an inert gas which is preferably nitrogen, but may be a mixture ofinert gases containing nitrogen and carbon dioxide. Such mixtures may beobtained in the process by burning of residual carbonaceous materialremaining on the oil shale after retorting and provide heat for theretorting operation. Other gases which may be used include the inertnormally gaseous hydrocarbons such as methane, ethane, propane, mixturesthereof, argon, krypton, neon, and the like.

The pressure on the retorting zone is suitably in excess of 250 p.s.i.g.and may be within the range of 250 p.s.i.g. to about 2500 p.s.i.g. Below250 p.s.i.g. the effect of pressure with an inert gas is notsignificant. Above 2500 p.s.i.g. pressure, the added benefits accruingto higher pressures than 2500, are marginal and are offset by the addedoperating problems and costs required. Hence, the range of about 250 toabout 2500 p.s.i.g. is considered to be necessary and important in thepractice of the present invention. The pressure in the other zones ofthe retorting system may be substantially below that of the retortingzone and allows use of less expensive equipment. It is not necessary touse high pressure except in the retorting zone because pressure has noeffect except in the retorting zone. Pressures in the other zones mayrange from 0i p.s.i.g. to 100 p.s.i.g.

DESCRIPTION OF THE DRAWING WITH REFER- ENCE TO THE PREFERRED'EMBODIMENTS Referring now to the drawing wherein a plural stageretorting system of crushed oil shale is described; numeral 11designates a preheating zone, numeral 12 is a retorting zone, numeral 13is a combustion zone, and numeral 14 is a cooling zone. Fresh oil shalehaving a Fischer Assay within the range from 15 to 70 gal./ton is fedinto zone 11 by line 15 wherein the crushed shale is preheated bycontact lwith gas introduced by line 16 connection into a distributingmeans 17. The crushed oil shale flows countercurrently to the gasintroduced by line 16 and is discharged by zone 11 by line 18 through asuitable control means 19 which may be a locked hopper- Star feedersystem into retorting zone 12 which may be maintained at a temperatureof about 600 F. to 900 F. Zones 11, 13 and 14 are suitably maintained ata range of about 0 p.s.i.g. to 100 p.s.i.g. wherein zone 12 ismaintained at a higher pressure in excess of 250 p.s.i.g. which mayrange from 250 p.s.i.g. to about 2500 p.s.i.g.

In zone 12 the preheated crushed shale is retorted in the presence ofinert gas introduced under pressure by line into a distributing means21. Line 20 contains a compressor 22 by way of which the pressure ofinert gas is raised to a pressure within the range given. The inert gasmay be introduced by way of line 23 controlled by valve 24 from a sourceoutside the system and thence into a furnace or heater 25 containingheat coils 26 and burners 27 and thence into line 20. The inert gas maybe obtained from line 28 which connects into combustion zone 1.3. Line28 connects to line 29 containing a valve 30 by -way of which excessilue gas may be discharged. The ue gas may be a mixture of nitrogen andcarbon dioxide resulting from burning residual carbonaecous material onthe oil shale introduced into Zone 13 by line 31 controlled by controlmeans such as valve 32 for reduction of pressure; the heat retorted oilshale being contacted with a free oxygen-containing gas such as airintroduced by line 33 controlled by valve 34 into distribution means 3S.The combustion operation in zone 13 produces the ue gas which iswithdrawn by line 29 and may be discharged at least in part by openingvalve 30 or recycled by line 23 to line 20` by opening or throttlingvalve 28a.

The burned oil shale substantially free of carbonaceous material is thendischarged by line 36 into cooling Zone 14 where it is contacted withinert gas at a lower temperature introduced by line 37 throughdistribution means 38 from a source which will be described further.

A portion of the gas from zone 113 or 14 may be introduced intopreheating zone 11 by withdrawing a portion of the fiue gas from zone 13by line 39 controlled by valve `40 which connects into line 16v or bywithdrawing a portion of the gas from zone 14 by way of line 41controlled by Valve 42. The gas from Zone 14 may be discharged from thesystem by closing valve 43 and opening valve 44 in line 41.

The product from retorting zone 12 is withdrawn by line 45 andintroduced by line 461 controlled by valve 47 which reduces the pressureof same into a drum 48 equipped with a cooling means 49` in the upperportion thereof. By virtue of the reduction of pressure and the coolingmeans 49, the temperature of the product is reduced which allows aseparation to be made between the shale oil which is recovered from zone48 by line 50 controlled by valve 51 for further processing and theinert gas and noncondensables which are withdrawn by line 52. A portionof the inert gas and noncondensables may be discharged from the systemby line 52 on opening valves 53 and S4. Preferably, however, the inertgas is recycled to line 23 by branch line 55 controlled by valve 56connecting to line 23 for heating or recompressing of same.

A portion of the inert gas is suitably recycled by line 57 controlled byvalve 58 to line 37 for introduction into cooling zone 14 where itserves to cool the retorted spent shale which is discharged from thesystem by line 59. When the inert gas is not introduced by line 57,valve 58 `would be closed and valve 60 in line 37 opened allowing gasfrom an extraneous source to be used.

The gas from the preheating zone 11 is withdrawn by line 61 and may bedischarged from the system by opening valve `62. Preferably, however,since this gas may contain valuable hydrocarbons, valve `62 remainsclosed and the gas in line 61 discharges by line 63 into line 46 andthence into zone 48.

From the foregoing description taken with the drawing representing apreferred mode and embodiment, it will be seen that crushed oil shalemay be retorted in a thermal system employing a plurality of stagesemploying an inert gas under pressure in the retorting Zone to obtain ashale oil of improved product quality; the oil recovered by line havinghigh gravity, a low viscosity, a low pour point, and a high hydrogen tocarbon ratio.

4 By virtue of retorting under high pressure with an inert gassubstantially improved and useful results are obtained.

EXAMPLES In order to illustrate the present invention further,comparative runs were made where crushed oil shale having particlediameters within the range from 3A; to 3 inches and an average FischerAssay value of 34.4 gal./ ton was retorted under the same conditionsexcept in one instance H2 pressure was used and the other instance N2pressure was employed. Runs at 750 and 33 p.s.i.g. were conducted, theresults and conditions of which are shown in Table I.

TABLE I Run Number .TRB

Retort gas H2 N2 H2 N2 Retort pressure, p 750 750 33 33 Shale lot number8 8 10 10 Oil inspections:

Gravity, API at 60 F 38. 9 36.5 26. 2 26. 1 Viscosity, cs. at F 1. 70 1.73 12. 06 10. 34 Pour point, F 20 20 85 85 Nitrogen, wt. percent- 1.40 1. 46 1. 68 1. 60 Hydrogen, wt. percent 12.33 12. 17 l1. 96 11. 84Carbon, wt. percent 81. 46 84.75 83. 83 82. 10

As can be seen from these data, gravity, viscosity and pour point arevery similar at the same pressure but significantly different aspressure is changed from 33 to 750 p.s.i.g. Thus, the type of gas had nomeasurable eiect on product quality but an increase in pressure gives amuch improved product; i.e., lower density, lower viscosity, lower pourpoint.

Thus, it will be clear that an unobvious result is obtained sincenitrogen retorting at high pressure gave substantially similar resultsto that obtained with hydrogen. Heretofore, it was thought that areactive gas at elevated pressure was necessary for such beneficialresults. The data in Table I show that beneficial results are obtainedwith an inert gas.

The reason for such unexpected results is not known, but nevertheless itis quite unexpected to obtain same. Such results are quite useful inthat cheap and readily available inert gas may be used in lieu of theexpensive and scarce hydrogen and yet obtain quite desirable results.

The nature and objects of the present invention having been completelydescribed and illustrated, and the best mode `and embodimentcontemplated set forth, what we wish to claim as new and useful andsecure by Letters Patent is:

1. In a plural stage thermal operation for recovering shale oil fromcrushed oil shale in which the crushed shale moves serially downwardlythrough vertical preheating, retorting, burning, and cooling zones andin which shale oil is formed, the method which comprises:

maintaining said retorting zone at a retorting temperature byintroducing a heated inert gas thereto under a pressure in excess of 250p.s.i.g.;

recovering from said retorting zone a product containing shale oil andsaid inert gas;

separating inert gas from said recovered product;

returning at least a portion of said separated inert gas to saidretorting zone after heating and compressing same to said retortingtemperature and to said pressure in excess of 250 p.s.i.g.; and

the other zones of said plural stage thermal operation being maintainedat a pressure substantially below the pressure of said retorting zone.

2. A method in accordance with claim 1 in which the pressure on theretorting zone is within the range from about 250 to `about 2500p.s.i.g.

3. A method in accordance with claim 1 in which the inert gas isnitrogen.

4. A method in accordance with claim 1 in which the inert gas is fluegas.

5. A method in accordance with claim 1 in which the inert gas is anoncondensable hydrocarbon.

6. A method in accordance with claim 1 in which the inert gas is carbondioxide.

7. A method in accordance with claim 1 in which the retortingtemperature is within the range of about 600 F. to about 1000o F.

8. A method in accordance with claim 1 in which:

(a) the pressure on the retorting zone is within the range from about250 to about 2500 psig.;

(b) the inert gas comprises nitrogen; and

(c) the retorting temperature is Within the range of about 600 F. toabout 1000 F.

9. A method in accordance with claim 8 in which:

(a) the inert gas is flue gas;

(b) the flue gas is obtained from the combustion zone;

(c) the flue gas is compressed to said pressure; and

(d) the product is recovered by reducing its presssure and cooling same.

References Cited UNITED STATES PATENTS 3,224,954 12/ 1965 Schlinger etal 208-11 2,768,937 10/1956` Wigton 201--29X 3,475,3 19 10/1969 MacLaren208--11 3,484,364 12/1969 Hemminger 208-11 3,489,672 1/1970 Schulman eta1. 208-1l CURTIS R. DAVIS, Primary Examiner U.S. Cl. X.R.

10. A method in accordance with claim 8 in which 20 20L-29 35

